1. Main technical content
High-strength steel bars refer to ordinary hot-rolled ribbed steel bars (HRB) and fine-grained hot-rolled ribbed steel bars (HRBF) with yield strengths of 400MPa and 500MPa, as specified in the current national standard. Ordinary hot-rolled steel bars (HRB) are often produced using microalloying processes involving V, Nb, or Ti. This mature process offers stable product quality and excellent overall performance. Fine-grained hot-rolled steel bars (HRBF) achieve ultrafine microstructures through controlled rolling and cooling processes, thereby improving steel performance without increasing alloy content. The welding process requirements for fine-grained hot-rolled steel bars are higher than those for ordinary hot-rolled steel bars, and this consideration should be taken into account in their application. After years of technical research, product development, and market promotion, 400MPa-grade steel bars have gained some application, and 500MPa-grade steel bars are beginning to be used.
High-strength steel bar application technologies mainly include design and application technology, steel bar replacement technology, steel bar processing and connection and anchoring technology, etc. 2. Technical indicators
The technical specifications of 400MPa and 500MPa grade steel bars should comply with the current national standard “Steel for Reinforced Concrete – Part 2: Hot-rolled Ribbed Bars” (GB1499.2). Design and application specifications should comply with the “Code for Design of Concrete Structures” (GB50010), the “Code for Acceptance of Construction Quality of Concrete Structures” (GB50204), the “Code for Construction of Concrete Structures” (New Edition), and other relevant standards. For steel bar diameters of 6 to 50mm, the standard yield strength of 400MPa grade steel bars is 400N/mm², the standard tensile strength is 540N/mm², and the design compressive strength is 360N/mm². For 500MPa grade steel bars, the standard yield strength is 500N/mm², the standard tensile strength is 630N/mm², and the design compressive strength is 435N/mm². For structures with seismic fortification requirements, seismic steel bars with the suffix “E” are recommended.
3. Scope of application
400MPa and 500MPa grade steel bars can be used in civil and industrial buildings and general structures in non-seismic and seismic fortification areas. They can be used as longitudinal force-bearing steel bars in reinforced concrete structural components and non-prestressed steel bars in prestressed concrete components, as well as stirrups and structural steel bars. The concrete strength grade of the corresponding structural beams, slabs and walls should not be lower than C25, and that of the columns should not be lower than C30.
4. Typical projects where this technology has been applied
400MPa-grade rebar is widely used in high-rise buildings, large public buildings, industrial plants, hydropower projects, bridges, and other structures in China. Typical projects include the Three Gorges Dam, the Beijing Olympics, the Shanghai World Expo, and the Sutong Yangtze River Highway Bridge. 500MPa-grade rebar is used in numerous projects, including the Hualin Dujiayuan project in Zhengzhou, Henan, the Hebei Construction Service Center, and the slag-free track slabs for the Beijing-Tianjin Intercity Railway.
3.2 Application technology of welded steel mesh 1. Main technical content
Welded steel mesh is a mesh-like steel product manufactured in a factory using specialized mesh welding machines. The longitudinal and transverse steel bars are arranged perpendicularly to each other at regular intervals, and all intersections are resistance spot welded using a multi-head spot welder with computerized automated production. The mechanical properties of the steel remain virtually unchanged before and after welding.
Currently, welded mesh is primarily made from CRB550 cold-rolled ribbed steel bars and HRB400 hot-rolled steel bars. Welded mesh is widely used and the technology is mature. This includes techniques for straightening and cutting steel bars, fabricating and distributing steel mesh, and designing, constructing, and installing the mesh.
The use of welded mesh can significantly improve the quality of steel bar projects, greatly reduce on-site steel bar installation hours, shorten construction periods, appropriately save steel, and has good comprehensive economic benefits. It is especially suitable for large-scale concrete projects.
2. Technical indicators
The technical indicators of steel welded mesh should comply with the requirements of GB/T1499.3 “Welded mesh for reinforced concrete” and JGJ114 “Technical specification for welded mesh concrete structure”. The diameter of cold-rolled ribbed steel bars should be 5 to 12 mm, and the strength standard should be 10 …
The standard value is 550 N/mm²; the diameter of hot-rolled steel bars should be 6-16 mm, and the standard yield strength value is 400 N/mm². The spacing between the bars in the direction of weld mesh fabrication should be 100, 150, or 200 mm, and the spacing between the bars perpendicular to the fabrication direction should be 100-400 mm. The maximum length of the weld mesh should not exceed 12 m, and the maximum width should not exceed 3.3 m. The shear resistance of the weld points should not be less than 0.3 times the specified yield strength of the tensile reinforcement of the specimen.
3. Scope of application
Cold-rolled ribbed steel welded mesh is widely used for reinforcement of cast-in-place reinforced concrete structures and precast components, particularly in floor slabs, roof panels, floors, walls, beam-column stirrups, and bridge deck pavement and pier crack prevention. It is also used for reinforcement of bi-block sleepers, track slab bases, and box girder top pavement in high-speed railways. It can also be used for reinforcement of tunnel linings, water pipelines, harbor terminals, and piles.
HRB400 grade steel welded mesh has good ductility of steel bars. In addition to being used in general reinforced concrete slab structures, it is more suitable for reinforcement of components with higher seismic fortification requirements (such as potential strong bottom reinforcement areas).
4. Typical projects where this technology has been applied
There are many projects in China that use welded mesh, with the most common applications being in the Pearl River Delta, the lower reaches of the Yangtze River (including Shanghai), and Beijing and Tianjin, such as the Beijing Bairong World Trade Center and the Shenzhen Civic Center project.